Hello, dear "user49915" :)
Polylang strings are meant to translate what themes and plugins save into the database, you know, into their configuration screen...
If the placeholder is not in this list, it will be in the php files. To translate these contents, you should look at the translation files (.po) of the theme and plugins.
(https://polylang.pro/doc/strings-translation/)
Usually, these files get located in the folders:
1.Themes
wp-content/languages/themes/{nome-do-tema}/{nome-do-tema}-{idioma}.po
2.Plugins
wp-content/languages/plugins/{nome-do-plugin}/{nome-do-plugin}-{idioma}.po
If the file does not exist, you can copy the file . po from the theme /Languages/ folder or plugin and paste there.
To edit a file. po you can use:
When you save the file, these tools have created a binary file (.mo) that will finally be read by Wordpress, following the logic of the folder paths I mentioned.
If you feel curious, the link below has the form that developers do to internationalize your themes or plugins:
https://codex.wordpress.org/I18n_for_WordPress_Developers